US11973531B2 - Optical communication system and master station - Google Patents
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- US11973531B2 US11973531B2 US17/916,789 US202017916789A US11973531B2 US 11973531 B2 US11973531 B2 US 11973531B2 US 202017916789 A US202017916789 A US 202017916789A US 11973531 B2 US11973531 B2 US 11973531B2
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/27—Arrangements for networking
- H04B10/272—Star-type networks or tree-type networks
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/03—Arrangements for fault recovery
- H04B10/032—Arrangements for fault recovery using working and protection systems
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04B—TRANSMISSION
- H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
- H04B10/07—Arrangements for monitoring or testing transmission systems; Arrangements for fault measurement of transmission systems
- H04B10/075—Arrangements for monitoring or testing transmission systems; Arrangements for fault measurement of transmission systems using an in-service signal
- H04B10/079—Arrangements for monitoring or testing transmission systems; Arrangements for fault measurement of transmission systems using an in-service signal using measurements of the data signal
- H04B10/0791—Fault location on the transmission path
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04J—MULTIPLEX COMMUNICATION
- H04J14/00—Optical multiplex systems
- H04J14/02—Wavelength-division multiplex systems
- H04J14/0278—WDM optical network architectures
- H04J14/0282—WDM tree architectures
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04J—MULTIPLEX COMMUNICATION
- H04J14/00—Optical multiplex systems
- H04J14/08—Time-division multiplex systems
Definitions
- the present invention relates to an optical communication system and a master station device in the optical communication system.
- a PON (Passive Optical Network) system is known as an optical communication system.
- TWDM-PON Time and Wavelength Division Multiplexing-PON
- WDM Widelength Division Multiplexing
- NPL 1 discloses a bus-topology WDM Access System as an example of a TWDM-PON system.
- the network topology of an OLT (Optical Line Termination, or Optical Line Terminal) and ONUs (Optical Network Units) is a bus topology.
- OLT Optical Line Termination, or Optical Line Terminal
- ONUs Optical Network Units
- bus topology WDM access system is applied to a MFH (Mobile Fronthaul) when deploying a mobile communication area linearly, for example.
- MFH Mobile Fronthaul
- NPL 2 discloses a protection method for improving reliability in a bus-topology WDM access system.
- a bus topology if the trunk fiber becomes disconnected, communication may be cut off for many ONUs.
- a loop-shaped communication path is formed by combining the main trunk fiber with a backup trunk fiber.
- the backup path is cut off by an optical switch, and communication between the OLT and ONUs is performed only via the normal path. If a disconnection occurs in a portion of the normal path, the backup path is enabled in addition to the normal path.
- the OLT uses the backup path to perform communication with disconnected ONUs that cannot perform communication via the normal path. This makes it possible to resume communication with all disconnected ONUs without waiting for repair of the optical fiber that constitutes the normal path.
- the master station device executes communication control processing for controlling communication with each of the slave station devices.
- this communication control processing is executed based on the “RTT” (Round Trip Time) between the master station device and each of the slave station devices.
- RTT Red Trip Time
- the master station device needs to be aware of the RTT for all of the slave station devices.
- uplink communication from multiple slave station devices (ONU) to a master station device (OLT) is performed using TDMA (Time Division Multiple Access).
- TDMA Time Division Multiple Access
- the OLT controls the transmission timing of the uplink optical signal from each ONU based on the corresponding RTT for that ONU.
- the OLT needs to be aware of the RTT for all of the communication partner ONUs in advance. Accordingly, when the OLT executes registration processing (discovery) for registering an ONU, the OLT measures the RTT for the ONU and holds the RTT together with other registration information.
- the OLT uses the backup path instead of the normal path to perform communication with disconnected ONUs that cannot perform communication via the normal path.
- performing registration processing for all of the disconnected ONUs and measuring the new RTTs takes a long time. In other words, the amount of time required to resume communication increases.
- One object of the present invention is to provide a technique for making it possible to shorten the time required for resuming communication in a protection method that uses a backup path in an optical communication system that includes a master station device and multiple slave station devices.
- a first aspect of the present invention relates to an optical communication system.
- the optical communication system includes:
- Communication paths between the master station device and each of the slave station devices include:
- the master station device is configured to execute communication control processing for controlling communication with each of the slave station devices based on an RTT (Round Trip Time) between the master station device and the slave station device.
- RTT Random Trip Time
- a normal path RTT is the RTT in a case of communication performed via the normal path.
- a backup path RTT is the RTT in a case of communication performed via the backup path.
- a first slave station device is a slave station device that cannot perform communication via the normal path, among the plurality of slave station devices.
- a first normal path RTT is the normal path RTT between the master station device and the first slave station device.
- a first backup path RTT is the backup path RTT between the master station device and the first slave station device.
- a first RTT is the RTT between the master station device and the loop path.
- a loop RTT is the RTT required for one full lap on the loop path.
- the master station device holds the normal path RTT for each of the slave station devices, the first RTT, and the loop RTT.
- the master station device executes the communication control processing with respect to the slave station devices based on the normal path RTTs.
- the master station device calculates the first backup path RTT based on the first RTT, the loop RTT, and the first normal path RTT, and resumes the communication control processing with respect to the first slave station device based on the calculated first backup path RTT.
- a second aspect of the present invention relates to a master station device that performs communication with each of a plurality of slave station devices in an optical communication system.
- the slave station devices are connected to a loop path in parallel.
- Communication paths between the master station device and each of the slave station devices include:
- the master station device is configured to execute communication control processing for controlling communication with each of the slave station devices based on an RTT (Round Trip Time) between the master station device and the slave station device.
- RTT Random Trip Time
- a normal path RTT is the RTT in a case of communication performed via the normal path.
- a backup path RTT is the RTT in a case of communication performed via the backup path.
- a first slave station device is a slave station device that cannot perform communication via the normal path, among the plurality of slave station devices.
- a first normal path RTT is the normal path RTT between the master station device and the first slave station device.
- a first backup path RTT is the backup path RTT between the master station device and the first slave station device.
- a first RTT is the RTT between the master station device and the loop path.
- a loop RTT is the RTT required for one full lap on the loop path.
- the master station device holds the normal path RTT for each of the slave station devices, the first RTT, and the loop RTT.
- the master station device executes the communication control processing with respect to the slave station devices based on the normal path RTTs.
- the master station device calculates the first backup path RTT based on the first RTT, the loop RTT, and the first normal path RTT, and resumes the communication control processing with respect to the first slave station device based on the calculated first backup path RTT.
- the master station device holds the normal path RTT for each slave station device, the first RTT between the master station device and the loop path, and the loop RTT required for one full trip on the loop path. If a first slave station device is detected, the master station device calculates a first backup path RTT for each first slave station device based on the first RTT, the loop RTT, and the first normal path RTT.
- the master station device then resumes communication control processing for each first slave station device based on the calculated first backup path RTT. It is not necessary to execute registration processing for all first slave station devices and directly measure the first backup path RTT. Accordingly, the time required to resume communication is shortened.
- FIG. 1 is a conceptual diagram schematically showing a configuration of an optical communication system according to an embodiment of the present invention.
- FIG. 2 is a conceptual diagram for describing normal operation of the optical communication system according to the embodiment of the present invention.
- FIG. 3 is a conceptual diagram for describing a situation in which a fiber has become disconnected in the optical communication system according to the embodiment of the present invention.
- FIG. 4 is a conceptual diagram for describing operations performed using a normal path and a backup path in the optical communication system according to the embodiment of the present invention.
- FIG. 5 is a conceptual diagram for describing a method of acquiring a backup path RTT for a disconnected ONU according to an embodiment of the present invention.
- FIG. 6 is a conceptual diagram showing an example of the configuration of an optical communication system according to an embodiment of the present invention.
- FIG. 7 is a conceptual diagram showing an example of the configuration of the master station device (OLT) in the optical communication system according to the embodiment of the present invention.
- FIG. 8 is a conceptual diagram for describing a method for measuring a first RTT and a loop RTT according to the embodiment of the present invention.
- FIG. 9 is a flowchart showing an example of processing performed by the optical communication system according to the embodiment of the present invention.
- FIG. 1 schematically shows the configuration of an optical communication system 10 according to the present embodiment.
- the optical communication system 10 includes a master station device 100 and multiple slave station devices 200 .
- m is an integer greater than or equal to 2.
- the master station device 100 is connected to the slave station devices 200 via an optical fiber and performs optical communication with each of the slave station devices 200 .
- the optical communication system 10 is a PON (Passive Optical Network) system.
- the master station device 100 is hereinafter referred to as an “OLT (Optical Line Termination, or Optical Line Terminal) 100 ”.
- the slave station devices 200 are hereinafter referred to as “ONUs (Optical Network Units) 200 ”.
- the network topology of the OLT 100 and the ONUs 200 is a bus topology. More specifically, as shown in FIG. 1 , the optical communication system 10 includes a loop path 300 that is formed by a trunk fiber arranged in a loop. The OLT 100 is connected to the loop path 300 . The ONUs 200 are connected to the loop path 300 in parallel.
- the loop path 300 Due to the inclusion of the loop path 300 , two types of communication paths exist between the OLT 100 and each of the ONUs 200 , namely a normal path PN and a backup path PS.
- the normal path PN is a communication path that extends in a first direction D 1 along the loop path 300 .
- the backup path PS is a communication path that extends in a second direction D 2 , which is opposite to the first direction D 1 , along the loop path 300 .
- FIG. 1 shows the normal path PN and the backup path PS for the ONU 200 - 1 as one example.
- FIG. 2 is a conceptual diagram for describing normal operation of the optical communication system 10 .
- the OLT 100 performs communication with each of the ONUs 200 via the normal path PN.
- the OLT 100 enables the normal path PN and disables the backup path PS.
- the OLT 100 executes “registration processing (discovery)” for registering the ONUs 200 in order to establish communication links with the ONUs 200 that are connected to the PON network.
- registration processing the OLT 100 detects the ONUs 200 that are connected to the PON network and assigns an identifier to each detected ONU 200 .
- the OLT 100 notifies the ONUs 200 of the assigned identifiers, and the ONUs 200 each hold the notified identifier.
- the OLT 100 executes “ranging processing” for measuring the round-trip propagation time (hereinafter referred to as RTT (Round Trip Time)) between the OLT 100 and each of the ONUs 200 .
- RTT Round Trip Time
- the OLT 100 executes “communication control processing” for controlling communication with each of the ONUs 200 .
- Uplink communication from the ONUs 200 to the OLT 100 is performed using the same wavelength through TDMA (Time Division Multiple Access).
- TDMA Time Division Multiple Access
- the OLT 100 determines a transmission timing and a transmission amount for the uplink optical signals from each of the ONUs 200 based on the corresponding RTTs of the ONUs 200 .
- the OLT 100 then generates transmission permission information that includes an identifier, a transmission timing, and a transmission amount for each of the ONUs 200 .
- the OLT 100 transmits the generated transmission permission information to each of the ONUs 200 .
- the transmission permission information reaches the ONUs 200 through the normal path PN.
- the ONUs 200 reference the identifiers included in the transmission permission information and identify a corresponding portion of the transmission permission information.
- the ONUs 200 each then transmit an uplink optical signal in accordance with the transmission timing and the transmission amount indicated by the transmission permission information.
- the uplink optical signals transmitted from the ONUs 200 reach the OLT 100 through the normal path PN.
- the OLT 100 holds an RTT for each of the ONUs 200 and executes communication control processing for controlling communication with the ONUs 200 based on the RTTs.
- the RTT for the case of communication via the normal path PN is hereinafter referred to as “normal path RTT”.
- the OLT 100 holds a normal path RTT for each of the ONUs 200 , and executes communication control processing for the ONUs 200 based on the normal path RTTs.
- FIG. 3 is a conceptual diagram for describing a situation in which a fiber has become disconnected in the normal path PN.
- a fiber disconnection occurs in the section between the ON 200 - 0 and the ONU 200 - 1 .
- communication with the ONUs 200 - 1 to 200 -( m ⁇ 1) is cut off.
- the ONUs 200 that cannot perform communication via the normal path PN are each hereinafter referred to as a “disconnected ONU 200 - j ”.
- a disconnected ONU 200 - j In the example shown in FIG.
- the above-described backup path PS is used in order to quickly resume (recover) communication with the disconnected ONUs 200 - j.
- FIG. 4 is a conceptual diagram for describing operations performed using the normal path PN and the backup path PS in the optical communication system 10 .
- the OLT 100 enables the backup path PS in addition to the normal path PN.
- the OLT 100 performs communication with that ONU via the normal path PN.
- the OLT 100 performs communication with those ONUs via the backup path PS instead of the normal path PN. This makes it possible to resume communication with all of the disconnected ONUs 200 - j without waiting for repair of the optical fiber that constitutes the normal path PN.
- the RTT for communication via the backup path PS is required in order to execute communication control processing for the disconnected ONUs 200 - j .
- the RTT for communication via the backup path PS is hereinafter referred to as the “backup path RTT”.
- the OLT 100 Before the start of communication performed via the backup path PS, the OLT 100 needs to be aware of the backup path RTT for all of the disconnected ONUs 200 - j . In other words, it is necessary to switch the RTT for all of the disconnected ONUs 200 - j from the normal path RTT to the backup path RTT.
- the present embodiment provides a technique capable of quickly acquiring the backup path RTT for all disconnected ONUs 200 - j.
- FIG. 5 is a conceptual diagram for describing a method of acquiring a backup path RTT for a disconnected ONU 200 - j.
- the OLT 100 is connected to a first branch point B 1 on the loop path 300 .
- a first RTT (T_trunk) is the RTT between the OLT 100 and the loop path 300 (i.e., the first branch point B 1 ).
- the disconnected ONU 200 - j is connected to a second branch point B 2 on the loop path 300 .
- a second RTT (T_branch) is the RTT between the disconnected ONU 200 - j and the loop path 300 (i.e., the second branch point B 2 ).
- a loop RTT (T_loop) is the RTT required for one full lap on the loop path 300 .
- a normal loop RTT (T_loop_n) is the RTT between the first branch point B 1 and the second branch point B 2 via the normal path PN.
- a backup loop RTT (T_loop_s) is the RTT between the first branch point B 1 and the second branch point B 2 via the backup path PS.
- the loop RTT (T_loop) is the sum of the normal loop RTT (T_loop_n) and the backup loop RTT (T_loop_s).
- T _loop T _loop_ n+T _loop_ s Expression 1
- the normal path RTT between the OLT 100 and the disconnected ONU 200 - j (first slave station device) is hereinafter referred to as the “first normal path RTT”.
- the backup path RTT between the OLT 100 and the disconnected ONU 200 - j is hereinafter referred to as the “first backup path RTT”.
- the first normal path RTT (Tj_normal) is the sum of the first RTT (T_trunk), the normal loop RTT (T_loop_n), and the second RTT (T_branch).
- the first backup path RTT (Tj_protect) is the sum of the first RTT (T_trunk), the backup loop RTT (T_loop_s), and the second RTT (T_branch).
- Tj _normal T _trunk+ T _loop_ n+T _branch Expression 2
- Tj _protect T _trunk+ T _loop_ s+T _branch Expression 3
- the first backup path RTT (Tj_protect) is expressed by Expression 4 shown below.
- Tj _protect 2 ⁇ T _trunk+ T _loop+2 ⁇ T _branch ⁇ Tj _normal Expression 4
- Tj_protect 2 ⁇ T _trunk+ T _loop ⁇ Tj _normal Expression 5
- the OLT 100 measures and holds the first RTT (T_trunk) and the loop RTT (T_loop) in advance.
- the first normal path RTT (Tj_normal) has been measured in the above-mentioned registration processing, and is known. Even after a disconnected ONU 200 - j is detected, the OLT 100 holds the registration information (an identifier and a first normal path RTT) for that disconnected ONU 200 - j instead of deleting it. Accordingly, the OLT 100 can calculate the first backup path RTT (Tj_protect) for all disconnected ONUs 200 - j based on the first RTT (T_trunk), the loop RTT (T_loop), and the first normal path RTT (Tj_normal). For example, the OLT 100 calculates the first backup path RTT (Tj_protect) for each disconnected ONU 200 - j according to Expression 5 shown above.
- the OLT 100 calculates the first backup path RTT for each disconnected ONU 200 - j based on the first RTT, the loop RTT, and the first normal path RTT. It is not necessary to execute registration processing and directly measure the first backup path RTT for all of the disconnected ONUs 200 - j . After the first backup path RTTs are calculated, the OLT 100 resumes communication control processing for the disconnected ONUs 200 - j based on the calculated first backup path RTTs. Note that given that the identifier of the disconnected ONU 200 - j does not change, the identifier does not need to be updated.
- the OLT 100 may set a slightly longer Grant period for the disconnected ONU 200 - j.
- the OLT 100 may periodically measure and update the first backup path RTT. Accordingly, the accuracy of the first backup path RTT is further improved.
- the plurality of ONUs 200 are connected to the loop path 300 in parallel. Accordingly, there are two types of communication paths between the OLT 100 and the ONUs 200 , namely the normal path PN and the backup path PS. If there is a disconnected ONU 200 - j that cannot perform communication via the normal path PN, communication can be resumed using the backup path PS instead of the normal path PN. This makes it possible to resume communication with all of the disconnected ONUs 200 - j without waiting for repair of the optical fiber that constitutes the normal path PN.
- the OLT 100 holds the normal path RTT for each ONU 200 , the first RTT between the OLT 100 and the loop path 300 , and the loop RTT for the loop path 300 . If a disconnected ONU 200 - j is detected, the OLT 100 calculates the first backup path RTT for each disconnected ONU 200 - j based on the first RTT, the loop RTT, and the first normal path RTT. The OLT 100 the resumes communication control processing for each disconnected ONU 200 - j based on the calculated first backup path RTT.
- the RTT switching method according to the present embodiment does not interfere with communication on the normal path PN.
- optical communication system 10 according to the present embodiment is described in more detail.
- FIG. 6 is a conceptual diagram showing an example of the configuration of the optical communication system 10 according to the present embodiment.
- the optical communication system 10 is a TWDM-PON (Time and Wavelength Division Multiplexing-PON) system that employs wavelength division multiplexing (WDM) technology.
- TWDM-PON Time and Wavelength Division Multiplexing-PON
- WDM wavelength division multiplexing
- the optical branching/coupling units 410 and 420 - i are optical splitters (power splitters), for example.
- the OLT 100 is connected to the optical branching/coupling unit 410 via the trunk fiber 310 .
- the trunk fiber 310 is branched into a main trunk fiber 300 N and a backup trunk fiber 300 S.
- the loop path 300 is formed by connecting the main trunk fiber 300 N and the backup trunk fiber 300 S in a loop.
- the communication path constituted by the main trunk fiber 300 N corresponds to the above-described normal path PN.
- the communication path constituted by the backup trunk fiber 300 S corresponds to the above-described backup path PS.
- the ONUs 200 - i are connected to the loop path 300 (main trunk fiber 300 N) in parallel. More specifically, the optical branching/coupling units 420 - i are arranged in order on the main trunk fiber 300 N. The ONUs 200 - i are respectively connected to the optical branching/coupling units 420 - i via branch fibers 320 - i . Preferably, the branch fibers 320 - i have substantially the same length. Here, “substantially the same length” means that the lengths are the same, or that the variation in length is small enough to be ignored.
- the optical branching/coupling unit 410 distributes downlink optical signals from the trunk fiber 310 to the main trunk fiber 300 N and the backup trunk fiber 300 S.
- the optical branching/coupling unit 410 also outputs uplink optical signals from the main trunk fiber 300 N and the standby trunk fiber 300 S to the trunk fiber 310 .
- the optical branching/coupling unit 410 corresponds to the first branch point B 1 shown in FIG. 5 .
- the optical branching/coupling units 420 - i each distribute optical signals from the trunk fiber on one side to the trunk fiber and the branch fibers 320 - i on the other side.
- the optical branching/coupling units 420 - i each also distribute optical signals from the branch fibers 320 - i to the trunk fibers on both sides.
- the optical branching/coupling unit 420 - i corresponds to the second branch point B 2 shown in FIG. 5 .
- the optical switch 430 is provided on the standby trunk fiber 300 S.
- the optical switch 430 enables/disables the backup path PS by allowing/blocking the passage of optical signals on the backup trunk fiber 300 S.
- the setting of this optical switch 430 is switched by the OLT 100 .
- the optical communication system 10 further includes a measurement assist device 500 .
- the measurement assist device 500 is provided on the loop path 300 at a position adjacent to the optical branching/coupling unit 410 .
- the measurement assist device 500 is provided on the backup trunk fiber 300 S that is adjacent to the optical branching/coupling unit 410 .
- This measurement assist device 500 is used to measure the first RTT and the loop RTT described above. A method for measuring the first RTT and the loop RTT using the measurement assist device 500 will be described later.
- FIG. 7 is a conceptual diagram showing an example of the configuration of the OLT 100 .
- n is an integer greater than or equal to 2.
- the channel termination devices 110 are also called an OLT-CT (Channel Termination) or an OSU (Optical Subscriber Unit).
- Different wavelengths are assigned to the channel termination devices 110 - x .
- the channel termination devices 110 - x perform communication using optical signals that have different wavelengths. More specifically, the channel termination devices 110 - x each perform downlink communication using a downlink optical signal that has a wavelength ⁇ Dx , and perform uplink communication using an uplink optical signal that has a wavelength ⁇ Ux .
- the wavelength ⁇ Dx and the wavelength ⁇ Ux are different wavelengths.
- the wavelength multiplexer/demultiplexer 120 is connected to each of the channel termination devices 110 - x .
- the wavelength multiplexer/demultiplexer 120 combines the wavelength ⁇ Dx downlink optical signals output from the channel termination devices 110 - x to generate a downlink WDM signal, and outputs the downlink WDM signal to the trunk fiber 310 .
- the downlink WDM signal is distributed to each of the ONUs 200 - i.
- the ONUs 200 - i each have a variable wavelength and are assigned to one of the channel termination devices 110 - x (wavelength ⁇ Dx , ⁇ Ux ).
- the ONUs 200 - i each extract the downlink optical signal that has the corresponding assigned wavelength ⁇ Dx from the downlink WDM signal.
- the ONUs 200 - i each transmit an uplink optical signal that has the corresponding assigned wavelength ⁇ Ux .
- the wavelength multiplexer/demultiplexer 120 demultiplexes uplink optical signals having various wavelengths from the trunk fiber 310 , and outputs the uplink optical signals having the wavelengths ⁇ Ux to the channel termination devices 110 - x . In this way, communication is performed between the channel termination devices 110 - x and the ONUs 200 - i.
- connection distances between the wavelength multiplexer/demultiplexer 120 and each of the channel termination devices 110 - x are substantially the same connection distance.
- substantially the same connection distance means that the connection distances are the same, or that the variation in the connection distance is small enough to be ignored.
- the channel termination device 110 includes a control unit 111 .
- the control unit 111 performs registration processing (discovery) and registers one or more ONUs 200 that are to be communication partners.
- the control unit 111 includes a storage unit 113 .
- the storage unit 113 stores the identifiers of the communication partner ONUs 200 in association with RTTs.
- the control unit 111 also performs communication control processing for controlling communication with the ONUs 200 . Specifically, the control unit 111 determines a transmission timing and a transmission amount for an uplink optical signal from each of the ONUs 200 based on the corresponding RTTs of the ONUs 200 . The control unit 111 then generates transmission permission information (Grant) that includes an identifier, a transmission timing, and a transmission amount for each of the ONUs 200 . The control unit 111 transmits the generated transmission permission information to each of the ONUs 200 . The ONUs 200 each transmit an uplink optical signal in accordance with the transmission timing and the transmission amount indicated by the transmission permission information.
- transmission permission information Grant
- the control unit 111 further includes an abnormality detection unit 115 .
- the abnormality detection unit 115 detects fiber disconnection in the normal path PN (main trunk fiber 300 N). In other words, the abnormality detection unit 115 detects a disconnected ONU 200 - j that cannot perform communication via the normal path PN.
- the abnormality detection unit 115 monitors the reception status of uplink optical signals from the transmission partner ONUs 200 . If an uplink optical signal is not received from an ONU 200 within a certain period of time after the transmission permission information is transmitted, the abnormality detection unit 115 determines that the corresponding ONU 200 has become a disconnected ONU 200 - j.
- the abnormality detection unit 115 may determine that fiber disconnection has occurred if uplink optical signals from multiple ONUs 200 are interrupted at substantially the same time (within a certain period of time) and a DyingGasp signal has not been received. As yet another example, the abnormality detection unit 115 may determine that fiber disconnection has occurred if uplink optical signals from multiple ONUs 200 farther than a certain distance (RTT) are interrupted at substantially the same time (within a certain period of time). As still another example, the abnormality detection unit 115 may detect fiber disconnection by performing a test using an OTDR (Optical Time Domain Reflectometer).
- OTDR Optical Time Domain Reflectometer
- each of the channel termination devices 110 (control units 111 ) is realized by an optical transceiver that transmits and receives optical signals, a controller that controls the optical transceiver and performs various types of information processing, and the like.
- the controller includes a processor and memory.
- the functionality of the channel termination device 110 is realized by the processor executing a communication control program stored in the memory.
- the communication program may be recorded on a computer-readable recording medium.
- the controller may be realized with use of hardware such as an ASIC (Application Specific Integrated Circuit), a PLD (Programmable Logic Device), or an FPGA (Field Programmable Gate Array).
- the measurement assist device 500 is provided on the backup trunk fiber 300 S that is adjacent to the optical branching/coupling unit 410 .
- the measurement assist device 500 has a function of, after receiving a measurement frame Fm, immediately sending the measurement frame Fm back to the OLT 100 .
- the measurement assist device 500 directly passes (transmits) normal PON frames that are different from the measurement frame Fm.
- the OLT 100 transmits the measurement frame Fm.
- the optical branching/coupling unit 410 distributes the measurement frame Fm to the main trunk fiber 300 N side and the backup trunk fiber 300 S side.
- the measurement frame Fm distributed to the backup trunk fiber 300 S side is hereinafter referred to as the measurement frame Fma for convenience.
- the measurement frame Fm distributed to the main trunk fiber 300 N side is hereinafter referred to as the measurement frame Fmb for convenience.
- the measurement assist device 500 adjacent to the optical branching/coupling unit 410 Upon receiving the measurement frame Fma, the measurement assist device 500 adjacent to the optical branching/coupling unit 410 immediately sends the measurement frame Fma back to the OLT 100 .
- the measurement frame Fma reaches the OLT 100 via the optical branching/coupling unit 410 .
- the OLT 100 calculates, as the first RTT (T_trunk), the time period from the transmission time of the measurement frame Fm to the reception time of the measurement frame Fma.
- the measurement frame Fmb propagates on the loop path 300 in the first direction D 1 and reaches the measurement assist device 500 .
- the measurement assist device 500 Upon receiving the measurement frame Fmb, the measurement assist device 500 immediately sends the measurement frame Fmb back to the OLT 100 .
- the measurement frame Fmb propagates on the loop path 300 in the second direction D 2 and reaches the OLT 100 via the optical branching/coupling unit 410 .
- the OLT 100 calculates, as a third RTT, the time period from the transmission time of the measurement frame Fm to the reception time of the measurement frame Fmb.
- the third RTT is the sum of the first RTT (T_trunk) and the loop RTT (T_loop). Accordingly, the OLT 100 can calculate the loop RTT (T_loop) based on the first RTT and the third RTT.
- FIG. 9 is a flowchart showing an example of processing performed by the optical communication system 10 according to the present embodiment.
- step S 1 the OLT 100 enables the backup path PS by operating the optical switch 430 .
- One channel termination device 110 - r transmits the measurement frame Fm and measures the first RTT (T_trunk) and the loop RTT (T_loop) using the technique illustrated in FIG. 8 .
- the channel termination device 110 - r holds the acquired first RTT (T_trunk) and loop RTT (T_loop) in the storage unit 113 .
- the OLT 100 disables the backup path PS by operating the optical switch 430 .
- step S 2 the channel termination device 110 - r notifies other channel termination devices 110 - s (s #r) of the first RTT (T_trunk) and the loop RTT (T_loop).
- each channel termination device 110 - x registers one or more ONUs 200 that are communication partners. At this time, the channel termination device 110 - x measures the normal path RTT for each ONU 200 and assigns an identifier to each ONU 200 .
- the normal path RTTs and the identifiers of the ONUs 200 are stored in the storage unit 113 . In other words, each channel termination device 110 - x holds the normal path RTTs and identifiers of the registered ONUs 200 in the storage unit 113 .
- step S 10 the channel termination devices 110 - x each perform communication with the registered ONUs 200 via the normal path PN. At this time, the channel termination device 110 - x executes communication control processing for the ONUs 20 based on the held normal path RTTs. Note that the channel termination devices 110 - x may periodically measure and update the normal path RTTs.
- step S 20 the channel termination devices 110 - x (abnormality detection units 115 ) determine whether or not fiber disconnection has occurred in the normal path PN. In other words, the channel termination devices 110 - x determine whether or not a disconnected ONU 200 - j has appeared. If a disconnected ONU 200 - j does not exist (No in step S 20 ), the processing returns to step S 10 . On the other hand, if at least one disconnected ONU 200 - j is detected (Yes in step S 20 ), the processing proceeds to step S 21 . Note that even after a disconnected ONU 200 - j is detected, the corresponding channel termination device 110 - x holds the registration information (identifier and first normal path RTT) for the disconnected ONU 200 - j instead of deleting it.
- step S 21 the OLT 100 enables the backup path PS in addition to the normal path PN by operating the optical switch 430 .
- step S 22 the channel termination device 110 - z that is performing communication with the disconnected ONU 200 - j switches the RTT for the disconnected ONU 200 - j .
- the channel termination device 110 - z calculates the first backup path RTT (Tj_protect) based on the first RTT (T_trunk), the loop RTT (T_loop), and the first normal path RTT (Tj_normal) that are held.
- the channel termination device 110 - z calculates the first backup path RTT (Tj_protect) according to Expression 5.
- the channel termination device 110 - z then switches the RTT for the disconnected ONU 200 - j from the first normal path RTT (Tj_normal) to the first backup path RTT (Tj_protect). Note that given that the identifier of the disconnected ONU 200 - j does not change, the identifier does not need to be updated.
- step S 30 the channel termination device 110 - z resumes communication by performing communication with the disconnected ONU 200 - j via the backup path PS. More specifically, the channel termination device 110 - z resumes communication control processing with respect to the disconnected ONU 200 - j based on the first backup path RTT that was calculated in step S 22 .
- the channel termination device 110 - z may set a slightly longer Grant period for the disconnected ONU 200 - j.
- the channel termination device 110 - z may periodically measure and update the first backup path RTT. Accordingly, the accuracy of the first backup path RTT is further improved.
- the optical communication system 10 according to the present embodiment is not limited to being a PON system.
- the technique according to the present embodiment can be applied to any optical communication system that has a loop path 300 and executes communication control processing based on RTT.
- the optical communication system 10 is applicable to, for example, a mobile fronthaul (MFH) in the case where a mobile communication area is deployed linearly or in a plane.
- MHF mobile fronthaul
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- Computing Systems (AREA)
- Small-Scale Networks (AREA)
- Optical Communication System (AREA)
Abstract
Description
- [NPL 1] Harada et al., “Cyclic Wavelength Allocation Scheme Reducing the Number of Wavelengths in Bus-Topology WDM Access Systems,” IEICE (Institute of Electronics, Information and Communication Engineers) 2020, B-8-12, p. 159, March 2020.
- [NPL 2] Ujikawa et al., “Protection Architecture for Reliable Bus-topology WDM Access Systems,” IEICE (Institute of Electronics, Information and Communication Engineers) 2020, B-8-14, p. 161, March 2020.
-
- a plurality of slave station devices that are connected to a loop path in parallel; and
- a master station device that is connected to the loop path and configured to perform communication with each of the slave station devices.
-
- a normal path that extends along the loop path from the master station device to each of the slave station devices in a first direction, and
- a backup path that extends along the loop path from the master station device to each of the slave station devices in a second direction that is opposite to the first direction.
-
- a normal path that extends along the loop path from the master station device to each of the slave station devices in a first direction, and
- a backup path that extends along the loop path from the master station device to each of the slave station devices in a second direction that is opposite to the first direction.
T_loop=T_loop_n+
Tj_normal=T_trunk+T_loop_n+
Tj_protect=T_trunk+T_loop_s+
Tj_protect=2×T_trunk+T_loop+2×T_branch−Tj_normal Expression 4
Tj_protect=2×T_trunk+T_loop−Tj_normal Expression 5
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- 10 Optical communication system
- 100 OLT (master station device)
- 110 Channel termination device
- 111 Control unit
- 113 Storage unit
- 115 Abnormality detection unit
- 120 Wavelength multiplexer/demultiplexer
- 200 ONU (slave station device)
- 200-j Disconnected ONU
- 300 Loop path
- 300N Main trunk fiber
- 300S Backup trunk fiber
- 310 Trunk fiber
- 320 Branch fiber
- 410 Optical branching/coupling unit
- 420 Optical branching/coupling unit
- 430 Optical switch
- 500 Measurement assist device
- PN Normal path
- PS Backup path
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US20020109876A1 (en) * | 2001-02-12 | 2002-08-15 | Peter Van Eijk | Fast protection switching by snooping on upstream signals in an optical network |
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US20110268435A1 (en) * | 2009-01-13 | 2011-11-03 | Hitachi, Ltd. | Communication system, subscriber accommodating apparatus and communication method |
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JP2002185485A (en) | 2000-12-18 | 2002-06-28 | Mitsubishi Electric Corp | Optical ring network system, optical node unit, method of making optical ring network system redundant |
-
2020
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- 2020-04-09 US US17/916,789 patent/US11973531B2/en active Active
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US20020109876A1 (en) * | 2001-02-12 | 2002-08-15 | Peter Van Eijk | Fast protection switching by snooping on upstream signals in an optical network |
JP2002281109A (en) * | 2001-03-19 | 2002-09-27 | Nec Corp | Method for thresholding, thresholding system and optical subscriber terminating equipment |
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JP7359294B2 (en) | 2023-10-11 |
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